Thank you for the idea!
You could temporarily circumvent this by disabling the auto-reconnect on disconnect option. When you move off an untrusted network, the app disconnects and reconnects, although it may seem like the connection between the wifi network and LTE is maintained, it is not. Any time the network changes, VyprVPN will need to reconnect. Although, it does so quickly.
If you turn off auto-reconnect, the connection will break after jumping from wifi to LTE and it will not re-establish.
Auto connect when using unknown Wi-Fi networks was added in the 2.3 release:
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I agree. Especially when video and audio streaming is included in your provider contract than being connected to a VPN would kill you data volume.